Well, for now, being that he's still a lil guy and there's only one of him, a fluval 4plus should do you just fine. That's what I've got in my 50 gallon with two 3inch turts....it's not working as well now as they get bigger and make more of a mess but it should be just right for you.
Other things on my to buy list would be, a bask area, lighting (open for suggestions, please), heater, thermometer, and possibly some decor. I would also want some sort of stand and if I forgot something, please let me know. Also, do I want a top for the tank? Do they make tops with sockets for the lighting needed to care for turtles, or should I just go with a single fixture w/clip (mount) for the light.
I don't have a top on my tank. It's 3/4 full. I just make sure the water level isn't high enough that they can climb out. For a basking spot, I've had pretty good luck with the Zoo Med Floating Turtle Dock. One place that I know it can be found is PetSmart. I'm not familiar with the diff kinds of heaters. I think mine's a Tronic but I don't remember...as long as it works, right? For decor I use large river rocks (get them at the dollar store for $1 a bag) and plastic plants that suction to the side of the tank. Makes a good sleeping spot. For lighting (remember, you need uva AND uvb) I use the TRex Active UV Heat bulb (uva/uvb combo). It fits great in my clamp lamp and both can be found at Petsmart. As far as a stand, get a plain steel one. They're way cheaper than to wooden ones with the drawers/shelves underneath. Not as pretty, but works just the same.
That's all I can think of for now.....
Just out of curiousity, does the lil guy have a name?
The things that come to those who wait may be the things that were left by those who got there first - Steven Tyler